A security guard turn visitors away from the Smithsonian’s National Air and Space Museum in Washington, Tuesday, April 7, 2015, after widespread power outages cause many of the buildings along the National Mall to shut down temporarily. Widespread power outages ... more >

WASHINGTON (AP) - The U.S. Capitol building was running on a generator for a time, and Metro trains kept moving, but on emergency power.

Tourists were evacuated from museums. At the State Department during the daily press briefing, spokeswoman Marie Harf was forced to finish her comments in the dark. In the White House, President Barack Obama barely noticed Tuesday’s disruption.

All this was caused by problems at an electrical station 35 miles southeast of Washington that caused widespread power outages on Tuesday.

The mechanical failure occurred shortly before 1 p.m. Tuesday at a transfer station in Charles County, Maryland, that is controlled by utilities serving Washington and southern Maryland. Homeland security officials in Washington and Maryland said there was an explosion at the station, although the two utilities, Pepco and the Southern Maryland Electric Cooperative, could not immediately confirm that there was a blast or fire. No one was injured, the utilities said.

Many of the outages were brief, but some were longer and forced evacuations. Officials said a mechanical failure at a transfer station led to the outages, and terrorism was not suspected. Tens of thousands of customers lost power.

The outages affected the White House, the Capitol, museums, train stations and other sites.

At the White House, the interruption last only a few seconds before backup generators kicked on. The complex quickly went back onto regular power. Electricity in the press briefing room dipped around lunchtime, briefly darkening cubicles and blackening TV screens.

White House spokesman Josh Earnest said he was with President Barack Obama in the Oval Office when the power blip occurred, and they didn’t notice anything unusual.

Power in the U.S. Capitol building twice shut down briefly, and then came back on via generator.

Some traffic lights were out, and Metro said 14 of its 91 public transit stations were affected. Power to the trains remained on and trains were moving, Metro spokesman Dan Stessel said, but the affected stations were on emergency power, with dimmer lighting and nonworking elevators and escalators.

Some Smithsonian museums also lost power, were evacuated and closed to the public, including the popular National Air and Space Museum and the National Portrait Gallery, a spokeswoman said.

Thousands of tourists spilled from the museums onto the National Mall. It’s a busy time of year for tourism as spring brings both better weather and the National Cherry Blossom Festival, which draws thousands to look at the pink-budded trees.

Bill, 62, and Karen, 56, Smith, a retired couple visiting D.C. for a week from Canterbury, Connecticut, were in the National Air and Space Museum when the outage happened.

“We were looking for moon rocks and the lights showing the moon rocks went out,” Bill Smith said. “Then the lights flickered and an announcement came over saying everyone needed to evacuate. They didn’t say why.”

He said no one panicked or even seemed irritated, though the crowd speculated about what happened.

Jenni Swan, who was visiting from Savannah, Georgia, with her husband and two children, said they were eating in the museum’s atrium when security officers said the building was being evacuated.

“Honestly I think my kids are excited because of all the fire trucks and people leaving the building quickly,” she said.